Polyester tackifier and adhesive composition

ABSTRACT

The invention relates to a novel polyester tackifier, adhesive compositions comprising the tackifier and methods of preparation. More specifically, the polyester tackifier is obtainable by polymerising a mixture comprising a diacid or derivative thereof, a diol, and at least 6 molar % of an organic monofunctional compound, wherein the mixture is essentially free from compounds comprising more than two carboxylic acid groups or alcohol groups.

[0001] This invention relates to a novel polyester tackifier, adhesivecompositions comprising the tackifier and methods of preparation. Morespecifically, the polyester tackifier is obtainable by polymerising amixture comprising a diacid or derivative thereof, a diol, and at least6 molar % of an organic monofunctional compound, wherein the mixture isessentially free from compounds comprising more than two carboxylic acidgroups or alcohol groups.

BACKGROUND OF THE INVENTION

[0002] Synthetic polymers such as acrylic polymers have, for the mostpart, replaced naturally occurring materials such as animal glues,starches and vegetable gums in many adhesive applications. The key tothis replacement was the development and use of tackifier resins in theformulation with synthetic polymers, because they give the system theability to wet the substrate surface and thus form a strong bond.Without tackifiers in the adhesive formulation, the synthetic polymershave low tack and peel adhesive performance.

[0003] Various resinous materials have been suggested as tackifiers forsynthetic polymers. Examples of materials suggested include rosin,disproportionated rosin, rosin esters such as glycerol esters of rosinand pentaerythritol esters of rosin, aliphatic hydrocarbon resins frompetroleum, aromatic petroleum resins, DCPD resins, terpene resins,terpene/phenol resins and cumarone/indene resins.

[0004] Tackifiers are resins that can be considered as high viscositysolvents for the base polymer. The term tackifier therefore, cannot begiven to any material unless we relate that material to the product thatit tackifies.

[0005] Acrylic polymer compositions have long been used as adhesivecompositions, particularly in pressure sensitive adhesive (PSA)compositions. Common PSA compositions include a high-molecular-weightacrylic base polymer and a tackifying resin and when required,plasticizer, stabilizer, antioxidant, filler, coloring agent and thelike. PSA compositions should have a high initial tack so that theadhesive surface merely needs to be contacted and pressed to the surfaceto achieve bonding. There should be little or no requirement to hold theadhesive and substrate in position for any significant time while a bonddevelops.

[0006] In developing adhesive formulations one seeks the optimumcombination of several adhesive properties and since it is not generallypossible to achieve the optimum for every property it is necessary toobtain the best balance of properties for the particular use in mind. Ine.g. PSA compositions which are used in the label industry one tries tooptimise the loop tack and peel and at the same time provide an adhesivewhose component will not migrate during storage.

[0007] Nowadays mainly rosin derivatives, such as disproportionatedrosin acids, and hydrocarbon resins are commercially used as tackifiersfor adhesive compositions comprising acrylic polymers. The rosinderivatives have been preferred due to better compatibility withacrylics.

[0008] Initially most important were the solvent acrylics, butenvironmental, health and safety needs of industry have resulted indramatic growth in water borne adhesive compositions comprising acrylicpolymers. With increasing desirability of water borne systems and oftentheir demonstration of significant performance enhancements withtackifier resins, new tackifier resins suitable for these systems arebeing sought.

[0009] U.S. Pat. No. 5,120,781 discloses tackifiers for hot meltadhesive compositions. The tackifiers are produced by reacting rosin anda polyhydric alcohol under conditions effective to substantiallycomplete the esterification reaction. The resulting reaction product isthen reacted with an aromatic dibasic acid providing a tackifier with acontent of rosin above 78 weight %.

[0010] U.S. Pat. No. 4,981,939 refers to a binder for preparing tonerswhich are used for developing electrostatic images formed in the processof electrography. The toner comprises as the main component a polyestercomposed of a polybasic acid component and a polyhydric alcoholcomponent and a rosin modified polyhydric alcohol. The rosin modifiedpolyhydric alcohol is produced by reacting a polyhydric alcohol havingthree or more hydroxyl groups with a rosin resulting in a polyesternetwork (cross-linking).

[0011] WO 9942508 relates to low viscosity aromatic polyester polyolsprepared by reacting a phthalic acid based material with diethyleneglycol, a higher functional polyol having an average functionality ofgreater than two and a long chain alkyl acid, ester or oil. Theresulting aromatic polyester polyol is a branched polyester.

[0012] U.S. 3,438,918 refers to rubber compositions obtained by reactingpolyhydric alcohols, polybasic acids and oils.

[0013] Thus one advantage of the present invention is to provide atackifier which is compatible with water borne pressure sensitiveadhesive compositions and hot melt pressure sensitive adhesivecompositions.

[0014] The further advantage with the present invention is theimprovement of overall adhesive properties of adhesive compositions andspecifically improving the properties of loop tack and peel and at thesame time provide an adhesive (composition) which component(s) will notmigrate during storage.

[0015] A still further advantage with the present invention is toprovide a polyester tackifier comprising a minimum amount of rosinderived from natural sources thereby reducing the cost of production,i.e. a polyester which is capped at both ends with a monofunctionalcompound (a polyester containing not more than two rosin residues).

[0016] Another advantage with the present invention is to provide astraight chain polyester resin being solid or liquid.

[0017] Still further advantages of the present invention are disclosedby the following specification.

SUMMARY OF THE INVENTION

[0018] The present invention relates to a polyester tackifier and apressure sensitive adhesive composition comprising the polyestertackifier according to the claims. More specifically, the presentinvention relates to a polyester tackifier which is obtainable bypolymerising a mixture comprising a diacid or derivative thereof, adiol, and at least 6 molar % of an organic monofunctional compound,wherein the mixture is essentially free from compounds comprising morethan two carboxylic acid groups or alcohol groups and a pressuresensitive adhesive composition comprising said polyester tackifier. Thepresent invention also relates to the use of the polyester tackifier, anaqueous pressure sensitive adhesive composition, a hot melt pressuresensitive adhesive composition and a method for manufacturing apolyester tackifier.

[0019] The polyester tackifier is suitably obtained by esterification ofat least one diacid or derivative thereof, at least one diol, and atleast 6 molar % of an organic monofunctional compound, wherein themixture is essentially free from compounds comprising more than twocarboxylic acid groups or alcohol groups, i.e. suitably essentially freefrom compounds comprising more than two functional groups enabling thecompounds of taking part in the polymeric esterification reaction. Thediols and diacids preferably will produce an alternatinglinear/non-branched condensation polymer which is terminated at bothends by the organic monofunctional compound, the latter functioning as achain stopper, i.e. capper.

[0020] The diacids which can be used in the present invention areorganic diacids such as organic dicarboxylic acids or derivativesthereof. By derivatives thereof is meant acid anhydrides or any otheracid capable of forming an ester moiety in the polyester. Suitably, thedicarboxylic acids are aliphatic, cyclic or aromatic, whereby aromaticdicarboxylic acids or derivatives thereof are preferred. Even morepreferred are aromatic dicarboxylic acids having the dicarboxylic acidmoieties in para or ortho position such as terephthalic acid andphthalic acid. Aromatic dicarboxylic acids having the diacid moiety inortho position are especially favourable such as phthalic acid. Thealiphatic diacids can be branched or linear comprising from 4 up to 12carbon atoms. The term diacids also encompasses acid anhydrides whereappropriate as well as chlorides and esters of carboxylic acids.Examples of useful diacids are selected from the group comprisingterephthalic acid, isophthalic acid, phthalic acid, malonic acid,dimethyl malonic acid, succinic acid, glutaric acid, adipic acid,trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaicacid, sebacic acid, fumaric acid, maleic acid, itaconic acid, pimelicacid, 1,3-cyclopentanedicarboxylic acid, 1,2 cyclohexanedicarboxylicacid, 1,4-cyclohexanedicarboxylic acid, 2,5 norbornanedicarboxylic acid,1,4 naphthalic acid, diphenic acid, 4,4′-oxydibenzoicacid, diglycolicacid, 2,5-naphtalenedicarboxylic acid and/or mixtures thereof.

[0021] The diols, often also referred to as glycols, used in the presentinvention are preferably linear or branched aliphatic diols, cyclicdiols, aromatic diols, alkylene glycols or polyalkylene glycols ormixtures thereof, whereby alkylene glycols or polyalkylene glycols ormixtures thereof are especially preferred. Specific polyalkylene glycolsmay be polyethylene glycol and polypropylene glycol notably having from1 up to 4 repeating alkylene oxide units, more preferably from 2 up to 3repeating units. The polyoxyalkylene glycols may comprise both ethyleneoxide and propylene oxide unit. Suitable diols are selected from thegroup of ethylene glycol, propylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol and dipropylene glycol ormixtures thereof. Other suitable diols can be selected from the group of1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol,1,10-decanediol, 2-methyl-1,3-propanediol,2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol,2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol,3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,6-hexanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1,4-cyclohexanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol,4,4′-methylenediphenol, 4,4′-(2 -norbornyliden)-diphenol,4,4′-dihydroxybiphenol, o-, m-, p-dihydroxybenzene,4,4′-isopropylidenediphenol, 2,5-naphtalenediol, p-xylenediol,cyclopentane-1,2-diol, cyclohexane-1,2-diol, cyclohexane-1,4-diol,etherified diphenols such as bisphenol A-alkylene oxide adducts and/ormixtures thereof.

[0022] The organic monofunctional compounds used in the presentinvention are suitably monocarboxylic acids or monohydric alcohols.Preferably, the organic monofunctional compounds are monocarboxylicacids exemplified by rosins (colophonies) derived from natural sourcessuch as gum rosins, wood rosins and tall-oil rosins. These naturallyoccurring rosins are suitably mixtures and/or isomers of monocarboxylictricyclic rosin acids usually containing 20 carbon atoms. The tricyclicrosin acids differ mainly in the position of the double bonds. Typicallythe rosin is a mixture of substances comprising levopimaric acid,neoabietic acid, palustric acid, abietic acid, dehydroabietic acid,seco-dehydroabietic acid, tetrahydroabietic acid, dihydroabietic acid,pimaric acid, and isopimaric acid. The rosins derived from naturalsources also include rosins, i.e. rosin mixtures, modified notably bypolymerisation, isomerisation, disproportionation and hydrogenation.Furthermore, the rosins may be treated with an aldehyde, for exampleformaldehyde, giving a rosin alcohol. Apart from rosins, carboxylicacids, such as naphtenic acid, and carboxylic acid or alcoholfunctionalised petroleum resins (aliphatic and/or aromatic) can be used.The mixture comprises suitably at least 10 molar % of the organicmonofunctional compound, preferably, at least 15 molar %.

[0023] The polyester tackifier is suitably prepared by polymerising amixture comprising from 15 up to 45 molar %, based on total monomers,more preferably from 20 up to 40 molar % and most preferably from 30 upto 35 molar % of a diacid, from 30 up to 55 molar %, based on totalmonomers, more preferably from 40 up to 55 molar % and most preferablyfrom 45 up to 50 molar % of a diol, and from 6 up to 40 molar %, basedon total monomer, more preferably from 10 up to 40 molar % and mostpreferably from 15 up to 35 molar % of a monofunctional compound,wherein the mixture is essentially free from compounds comprising morethan two carboxylic acid groups or alcohol groups. Suitably, the mixtureis essentially free from any compound comprising more than twofunctionalities which can take part in the polymerisation reaction, i.e.compounds comprising more than two functionalities or derivativesthereof which can be contained in the polyester tackifier. Byessentially free is usually meant that the mixture comprises less than 5molar %, preferably less than 1 molar %, most preferably less than 0.1molar %, based on total monomers, of compounds comprising more than twocarboxylic acid groups or alcohol groups. Thus, the polyester tackifieris suitably a non-branched polyester. In case where an excess of diolover diacid is present in the monomer mixture, a monocarboxylic acidusually is employed as chain stopper to “cap” the polyester whereby amonocarboxylic acid (rosin) terminated polyester is obtained. In thereversed situation, excess diacid over diol present in the monomermixture, a monohydric alcohol can be employed as chain terminator to capthe polyester.

[0024] The polyester tackifier of the present invention is suitablyformed by a condensation polymerisation (esterification) carried out inan inert gas atmosphere. Furthermore, the condensation reaction may beconducted in the presence of catalytical amounts of at least oneesterification catalyst. Usually esterification catalysts includephosphoric acid, phosphorous acid, hypophosphorous acid, para-toluenesulfonic acid, lithium carbonate, calcium hydroxide, zinc oxide ormixtures thereof. Additionally, a disproportionation catalyst may bepresent if one or more rosins are employed. Examples ofdisproportionation catalyst can be supported or non-supported metalssuch as palladium, nickel and platinum and furthermore iodine, iodides,sulfides, mono- and poly phenol sulfides (i.e. amylophenol sulfidepolymer). The esterification catalyst is generally present in amountsbetween about 0.01 and 0.1 weight %, notably between 0.05 and 0.07weight %; while the disproportionation catalyst usually is present inamounts between about 0.1 and 0.3%, all being weight percents based onthe weight of total monomers. In those embodiments utilisingesterification and/or disproportionation catalysts, the catalyst issuitably added after the building blocks have been molten.

[0025] The monomer mixture is generally polymerised at a temperatureranging from 150° C. up to 350° C., usually from 220° C. up to 280° C.,and most preferably from 250° C. up to 260° C. until distillation ofwater has ceased. Typically the reaction time may vary from 10 up to 30hour, more preferably from 12 up to 20 hour, and most preferably from 14up to 16 hours. The reaction usually is terminated when the acid valuehas dropped below 25 mg KOH/g and/or the acid value change has droppedbelow 1 mg KOH/g/hour.

[0026] The polyester resins according to the invention preferably havenumber average molecular weight (Mn) between 400 and 6000, morepreferably between 400 and 2000, and most preferably between 500 and1800. The molecular weight distribution of the resins, measured by thepolydispersity index generally ranges from 1.1 up to 2.0 and morepreferably from 1.1 up to 1.3.

[0027] The physical state of the polyester resin can be solid or liquidat ambient temperature depending on reaction conditions and monomersused, specifically which type of diols are used. The novel polyesterresins are suitably blended with other tackifiers such aspentaerythritol esters of rosin.

[0028] The present invention also refers to pressure sensitive adhesivecompositions comprising a polymer and the polyester tackifier describedabove. Pressure sensitive adhesive compositions comprising the polyestertackifier described above are especially advantageous for lowtemperature applications such as giving good adhesive properties whenused at temperatures well below 0° C. In addition, adhesive compositionscan be produced at lower cost with corresponding or improved tackifierproperties when all or part of the conventional tackifiers, e.g.tackifiers based on pentaerythritol, are substituted by the abovedefined novel polyester tackifier.

[0029] The present invention furthermore refers to the use of thetackifier for pressure sensitive compositions.

[0030] According to one preferred embodiment of the present inventionthe polyester tackifier is comprised in aqueous pressure sensitiveadhesive (PSA) compositions further containing other polymers.

[0031] The tackifier is preferably supplied in form of an aqueousdispersion. The tackifier is dispersed in water using dispersing agentssuch as ethoxylated phosphate ester surfactants. The amount ofdispersing agent used is usually from 2 up to 6 weight % based ontackifier. The polyester tackifier is suitably present in the aqueoustackifier dispersion in an amount from 40 up to 65 weight % based ontotal tackifier dispersion, more preferably from 50 up to 57 weight %.

[0032] The pressure sensitive adhesive compositions and the aqueousadhesive compositions according to the present invention comprisepolymers. Suitable polymers are exemplified by natural and syntheticrubbers such as polychloroprene rubber, styrene-butadiene rubbers, SISblock copolymers, SBS block copolymers, VAE (vinylacetate ethylenecopolymers), nitrile rubbers and polyisobutylene rubbers, acrylatepolymers, acrylic polymers such as acrylic esters and methacrylatepolymers or mixtures thereof.

[0033] Especially suitable polymers used in aqueous adhesivecompositions according to the invention are acrylic polymers and/oracrylic ester copolymers dispersed in an aqueous phase which can beobtained by emulsion polymerisation of a wide range of olefins andacrylates such as 2-ethylhexyl acrylate and butyl acrylate. The polymeris suitably present in the form of an aqueous polymer dispersion in anamount from 50 up to 70 weight % based on total polymer dispersion,preferably from 55 up to 65 weight %.

[0034] The aqueous adhesive composition usually comprises the tackifierdispersion in an amount from 10 up to 40 weight % based on total aqueouscomposition, preferably from 20 up to 30 weight %, and the polymerdispersion in an amount from 60 up to 90 weight % based on total aqueouscomposition, preferably from 70 up to 80 weight %.

[0035] Other compounds known to the person skilled in the art may alsobe comprised in the water borne adhesive composition exemplified byplasticisers, stabilisers, antioxidants, fillers, colouring agent andthe like.

[0036] According to a further preferred embodiment, the polyester resintackifier is comprised in a hot melt pressure sensitive adhesive (PSA)composition. Accordingly, the present invention encompasses hot meltpressure sensitive adhesive composition comprising the above definedpolyester tackifier. The hot melt compositions, preferably containspolymer resins including ethylenic copolymers of ethylene and othervarious monomers such as vinyl acetate, methyl acrylate, ethyl acrylateand other acrylates. In addition, styrenic block copolymers (SBC), suchas SBS, styrene-isoprene-styrene (SIS) andstyrene-ethylene-butylene-styrene (SEBS) are employed in the presentinvention. EVA and SBS based copolymers are particularly preferred.

[0037] In addition, ethylenic copolymer-based hot melt compositions maycomprise mineral waxes such as paraffin wax and microcrystalline wax andsynthetic waxes such as polyethylene wax and polypropylene wax. Otheranimal or vegetable waxes may also be used.

[0038] Preferred examples of oil used in the SBC-based hot meltcompositions of the present invention include mineral oils of relativelyhigh molecular weight and olefin oligomers. Other vegetable and/oranimal oils may be used.

[0039] The polyester tackifier is preferably added to the hot meltcomposition from 10 up to 60% by weight based on total composition morepreferably from 30 up to 60% by weight.

[0040] The styrenic block copolymers are suitably added from 10 up to75% by weight more preferably from 10 up to 40% by weight.

[0041] The wax may be added from 5 up to 50% by weight, suitably from 5up to 30% by weight.

[0042] The amount of polymers/copolymers and other compounds containedin the adhesive compositions, i.e. aqueous compositions or hot meltcompositions, is/are not critical and may vary so as to give thepreferred properties of the adhesive composition. The compounds can bein any physical state guided by the state of the adhesive compositionsuch as dispersed in an aqueous phase, liquid or solid.

[0043] The invention is further illustrated by the following examples,which, however, are not intended to limit the same. All units (parts orpercentages) are by weight unless otherwise indicated.

EXAMPLES OF THE INVENTION

[0044] Table 1 illustrates the product properties when using the rawmaterials stated therein. Abbreviations used in the table for thebuilding blocks (a), (b), and (c) are deg for diethylene glycol, mpdiolfor 2-methyl-1,3-propanediol, chdm for 1,4-cyclohexanedimethanol, megfor ethylene glycol, adipic for adipic acid, pza for phthalic anhydride,aze for azelaic acid, rosin for natural Chinese gum rosin, napht fornaphtenic acid, HCR for carboxylic acid functionalized petroleumhydrocarbon resins (e.g. Modified hydrocarbon resin AG-12-28 fromNeville Chemical Company), form ros for formaldehyde treated naturalChinese gum rosin. TABLE I Product properties of various polyesterresins Diol Diacid Capper No (a) (b) (c) Ratios Mn Mw/Mn Visco SP AVColor 1 Deg Adipic Rosin 34/33/33 840 1.2 525 — 24 10 2 Deg Pza Napht35/33/32 950 1.1 1600 — 13 12 3 Mpdiol Aze/pza Rosin 29/31/8/32 960 1.11900 — 18 6 4 Deg Pza Rosin 30/14/56 560 1.1 5150 — 20 4.5 5 Deg PzaRosin 34/33/33 870 1.1 11200 — 22 2 6 Deg Pza Rosin 40/51/9 1600 1.3200000 — 25 3.5 7 Meg Pza Rosin 24/38/38 740 1.1 — 44.7 15 4 8 Deg PzaHCR 26/36/38 1610 1.2 — 63.5 23 9 9 Deg Pza Form ros 19/9/72 680 1.2 —76.0 78 14 10 Chdm Pza Rosin 42/29/29 910 1.2 — 79.8 16 3

[0045] Entry no. 5 and 4 are described in more detail in example 1 and 2respectively. These examples illustrate the production and use astackifier of the polyester resins in more detail.

Example 1

[0046] A reaction vessel equipped with a nitrogen inlet, thermometer,stirrer and rectification column was charged with 500 g Chinese gumrosin, 505 g phthalic anhydride and 530 g diethylene glycol. Thereaction mixture was heated until a homogeneous melt resulted, then 2 gof Vultac 2 (Elf Atochem) disproportionation catalyst was added. Thetemperature was raised to 180° C. and held there for one hour. Then thetemperature was gradually increased to 250° C. The reaction wasconducted at that temperature for 20 hours and discontinued whendistillation of water ceased. A product was recovered with an acid valueof AV=22 mg KOH/g, a viscosity (brookfield at 50° C.) of 11200 mPa.s,number average molecular weight of Mn=870, and polydispersity ofMw/Mn=1.1. The color Gardner was 2.

[0047] 1500 g of this polyester resin was dispersed in water using theprocedure described in patent WO9412272 (U.S. Pat. No. 5,552,519). Thisyielded the tackifier dispersion (A).

[0048] Of this polyester resin 350 g was blended with 650 g of astabilised glycerol ester of rosin. This blend was then dispersed inwater with the aid of 60 g ethoxylated phosphate ester surfactant. Thisyielded the tackifier dispersion (B).

Example 2

[0049] A reaction vessel equipped with a nitrogen inlet, thermometer,stirrer and rectification column was charged with 800 g Chinese gumrosin, 200 g phthalic anhydride and 424 g diethylene glycol. Thetemperature is raised to 180° C. and held there for one hour. Then thetemperature is gradually increased to 250° C. The reaction was conductedat that temperature for 17 hours and discontinued when distillation ofwater ceased. A product was recovered with an acid value of AV=20 mgKOH/g, a viscosity (brookfield at 50° C.) of 5150 mPa.s, number averagemolecular weight of Mn=560, and polydispersity of Mw/Mn=1.1. The colorGardner is 4.5.

[0050] Of this polyester resin 700 g was blended with 300 g of apentaerythritol ester of rosin. This blend was then dispersed in waterwith the aid of 60 g ethoxylated phosphate ester surfactant. Thisyielded the tackifier dispersion (C).

Adhesive Test Results

[0051] Acronal V210, Primal EP5560, and Flexcryl 1625 are aqueousacrylic polymer dispersions available from respectively BASF, Rohm &Haas Co., and Air Products. Table 2 illustrates PSA performance usingstandard test methods (FINAT test methods for self-adhesive materials;Shear: FTM8, Peel: FTM1, Looptack: FTM9). Each adhesive composition wasblended in aqueous form in parts by weight and coated onto siliconerelease liner. The coat weight is 20±1 g/sq.m. The coated films weredried for 3 minutes at 90° C. The films were transfer coated to 80 gramsplain paper facestock and were then covered with release paper andallowed to set overnight at room temperature and 50% humidity. TABLE 2Adhesive performance test result Peel Looptack Shear LDPE Card SteelLDPE System (hours) (N) (N) (N) (N) 100% Acronal V210 27.0 5.1 12.5 12.15.1 CF AF AF AF AF 70% Acronal V210/ 0.6 13.9 19.3 11.6 8.9 30%Tackifier Dispersion A AF/PD AF/sCF AF AF 70% Acronal V210/ 6.3 13.220.1 17.3 10.7 30% Tackifier Dispersion B CF AF AF/sPT AF AF 70% AcronalV210/ 3.5 11.1 18.3 14.9 11.9 30% Tackifier Dispersion C CF AF/PD AF/sPTAF AF 100% Primal EP5560 11.2 2.6 4.0 9.1 3.0 CF AF AF AF AF 70% PrimalEP5560 1.0 4.6 14.3 8.3 4.5 30% Tackifier Dispersion A AF AF/sCF AF AF70% Primal EP5560/ 4.0 12.5 18.9 11.4 9.9 30% Tackifier Dispersion C CFAF/PD AF AF AF 100% Flexcryl 1625 19.3 5.3 14.6 9.9 5.3 AF AF AF AF 70%Flexcryl 1625 0.5 10.3 18.7 9.2 6.5 30% Tackifier Dispersion A AF/PDAF/sCF AF AF 70% Flexcryl 1625 1.3 13.0 20.1 16.0 10.6 30% TackifierDispersion B AF/PD AF/sCF AF AF

[0052] From the results in table 2 it can be concluded that thedispersions containing the novel polyester tackifiers have improvedadhesive properties in terms of peel and looptack.

1. A polyester tackifier, characterised in that the tackifier isobtainable by polymerising a mixture comprising a diacid or derivativethereof, a diol, and at least 6 molar % of an organic monofunctionalcompound, wherein the mixture is essentially free from compoundscomprising more than two carboxylic acid groups or two alcohol groups.2. A polyester tackifier according to claim 1 , characterised in thatthe tackifier is obtainable by polymerising a mixture comprising from 15up to 45 molar % of a diacid, from 30 up to 55 molar % of a diols, andfrom 6 up to 40 molar % of an organic monofunctional compound.
 3. Apolyester tackifier according to claim 1 , characterised in that themixture comprises from 6 molar % up to 40 molar % of an organicmonofunctional compound.
 4. A polyester tackifier according to claim 1 ,characterised in that the mixture comprises from 10 molar % up to 40molar % of an organic monofunctional compound.
 5. A polyester tackifieraccording to any of the preceding claims, characterised in that themixture comprises from 15 molar % up to 35 molar % of an organicmonofunctional compound.
 6. A polyester tackifier according to any ofthe preceding claims characterised in that the organic monofunctionalcompound is a monocarboxylic acid or monohydric alcohol.
 7. A polyestertackifier according to claim 6 , characterised in that the organicmonofunctional compound is a monocarboxylic acid.
 8. A polyestertackifier according to claim 7 characterised in that the monocarboxylicacid is a rosin derived from natural sources.
 9. A polyester tackifieraccording to any of the preceding claims characterised in that thetackifier is a non-branched polyester.
 10. A polyester tackifieraccording to any of the preceding claims characterised in that thediacid is an aromatic diacid.
 11. A polyester tackifier according to anyof the preceding claims characterised in that the diol is an alkyleneglycol or a polyalkylene glycol or mixture thereof.
 12. A pressuresensitive adhesive composition comprising a polymer and the polyestertackifier as defined by the claims 1 to 11 .
 13. Use of a polyestertackifier as defined by the claims 1 to 11 as a tackifier for pressuresensitive compositions.
 14. An aqueous pressure sensitive adhesivecomposition comprising a polymer and the polyester tackifier as definedby the claims 1 to 11 .
 15. A hot melt pressure sensitive adhesivecomposition comprising the polyester tackifier as defined by the claims1 to 11 .
 16. A method for manufacturing a polyester tackifier asdefined by the claims 1 to 11 , characterised in that the tackifier isproduced by polymerisation of monomers in an inert gas atmosphere at atemperature of from 150° C. up to 350° C.